1. Field of the Invention
The present invention relates to a calibration apparatus, a calibration method, and a program.
2. Description of the Related Art
An image projected by a projection apparatus such as a projector is distorted depending on a position or a geometry of a projection surface. Therefore, there is a technique of correcting the distortion. As this technique, a projected image is captured by a camera, a two-dimensional correspondence relationship between an image (hereinafter referred to as a projector image) projected by the projection apparatus and an image (hereinafter referred to as a camera image) captured by the camera is acquired, and the projection apparatus, an information processing apparatus corrects, or the like corrects the projected image so that an image without distortion is projected. Meanwhile, there is a technique of performing a three-dimensional measurement of a projection target and correcting the projector image using acquired three-dimensional information. The latter technique has an advantage that a user watching the projected image is hardly confined from watching depending on a watching position.
A process of requiring a correspondence between a projector image and a camera image is frequently performed in order to do the three-dimensional measurement. Here, a pattern light projected to a projection target by the projection apparatus is captured by the camera. A characteristic point is arranged in the pattern light. When the information processing apparatus or the like specifies corresponding characteristic points on the projector image and on the camera image, the three-dimensional measurement of the projection target can be performed using the triangular survey.
In order to do the three-dimensional measurement using the triangular survey, it is necessary to acquire an internal parameter (a focal length, a light axis position, a distortion of the lens, and so on) of the projection apparatus and the optical system of the camera and an external parameter (a relative position, and a posture) of the projection apparatus and the camera. A calibration is acquiring the internal parameter and the external parameter. There are various calibration methods.
However, there is a case where a difficulty exists in applying these calibration methods to a part of projectors. The optical systems of the projectors are classified into a pinhole model where a projection light from the projector passes through a specific point and a non-pinhole model where a projection light from the projector does not pass through a specific point. Because many of the above calibration methods are based on the pinhole model, it may be inappropriate to apply a calibration technique for the pinhole model to the projector having the optical system of the non-pinhole model misfitting the pinhole model.
Then, there is a calibration method applicable to projectors having an optical system of the non-pinhole model (for example, Patent Document 1). Patent Document 1 discloses a calibration apparatus configured such that the position of the projection target and the posture of the projection target are estimated based on the camera image, the reflection position at which a light beam projected by the projector reflects is estimated, and the direction of the light beam is identified based on the reflection position.
Patent Document 1: Japanese Laid-Open Patent Publication No. 2014-131091